Wearable audio device with head on/off state detection

ABSTRACT

Various implementations include wearable audio devices and related methods for controlling such devices. Some approaches include controlling a wearable audio device by: determining a magnitude of an acoustic transfer function based on an electrical signal from an internal microphone and an audio signal from an acoustic transducer at one or more predetermined frequencies; calibrating a proximity sensor; detecting a change in the state of the wearable audio device from one of: off-head to on-head, or on-head to off-head using both the calibrated proximity sensor and the magnitude of the acoustic transfer function; and adjusting at least one function of the wearable audio device in response to detecting the change from the on-head state to the off-head state or detecting the change from the off-head state to the on-head state.

PRIORITY CLAIM

This application is a continuation application of U.S. patentapplication Ser. No. 16/212,040, filed on Dec. 6, 2018, which is herebyincorporated by reference in its entirety.

TECHNICAL FIELD

This disclosure generally relates to wearable audio devices. Moreparticularly, the disclosure relates to determining the position of atleast one earpiece of a wearable audio device relative to a user, e.g.,the ear of a user. Operation of the wearable audio device may becontrolled according to the determined position.

BACKGROUND

Conventional approaches for detecting the on/off state of a wearableaudio device can be unreliable, resulting in false triggering ofdon/doff events or failure to detect such events. This false triggering,along with failure to detect don/doff events, can hinder the userexperience.

SUMMARY

All examples and features mentioned below can be combined in anytechnically possible way.

Various implementations include wearable audio devices with on/off statedetection. Additional implementations include methods of detecting theon/off state of wearable audio devices to control device functions. Aparticular approach includes: detecting a change from an on-head stateto an off-head state with a first sensor system; calibrating a second,distinct sensor system after detecting the change from the on-head stateto the off-head state; detecting a change from the off-head state to theon-head state using the calibrated second sensor system; and adjustingan operating state of at least one function of the wearable audio devicein response to detecting the change from the on-head state to theoff-head state or detecting the change from the off-head state to theon-head state

In some particular aspects, a wearable audio device includes: anacoustic transducer for providing audio playback of an audio signal to auser; an internal microphone acoustically coupled to an ear canal of auser, where the internal microphone generates an electrical signalresponsive to an acoustic signal incident at the internal microphone; aproximity sensor; and a control circuit coupled with the acoustictransducer, the internal microphone and the proximity sensor, thecontrol circuit configured to: determine a magnitude of an acoustictransfer function based on the electrical signal and the audio signal atone or more predetermined frequencies to detect a change in the wearableaudio device from an on-head state to an off-head state; calibrate theproximity sensor after detecting the change from the on-head state tothe off-head state; detect a change in the wearable audio device fromthe off-head state to the on-head state using the calibrated proximitysensor; and adjust at least one function of the wearable audio device inresponse to detecting the change from the on-head state to the off-headstate or detecting the change from the off-head state to the on-headstate.

In other particular aspects, a computer-implemented method of detectinga state of a wearable audio device on a user includes: detecting achange from an on-head state to an off-head state with a first sensorsystem, where the first sensor system includes an internal microphoneacoustically coupled to an ear canal of a user, the internal microphonegenerates an electrical signal responsive to an acoustical signalincident at the internal microphone, and the detecting of the changefrom the on-head state to the off-head state includes determining amagnitude of an acoustic transfer function based on the electricalsignal and the audio signal at one or more predetermined frequencies;calibrating a second, distinct sensor system after detecting the changefrom the on-head state to the off-head state; detecting a change fromthe off-head state to the on-head state using the calibrated secondsensor system, where the second sensor system includes a proximitysensor; and adjusting an operating state of at least one function of thewearable audio device in response to detecting the change from theon-head state to the off-head state or detecting the change from theoff-head state to the on-head state.

In additional particular aspects, a wearable audio device includes: anacoustic transducer for providing audio playback of an audio signal to auser; an internal microphone acoustically coupled to an ear canal of auser, where the internal microphone generates an electrical signalresponsive to an acoustic signal incident at the internal microphone;and a control circuit coupled with the acoustic transducer and theinternal microphone, the control circuit configured to: determine amagnitude of an acoustic transfer function based on the electricalsignal and the audio signal at one or more predetermined frequencies todetect a change in the wearable audio device from an on-head state to anoff-head state; pause the audio signal when the change from the on-headstate to the off-head state is detected; output an interrogation signalor narrowband noise at the acoustic transducer while the audio signal ispaused; determine a magnitude of an acoustic transfer function based onthe electrical signal and the interrogation signal or narrowband noiseat one or more predetermined frequencies to detect a change in thewearable audio device from the off-head state to an on-head state; andadjust at least one function of the wearable audio device in response todetecting the change from the on-head state to the off-head state ordetecting the change from the off-head state to the on-head state.

In further particular aspects, a wearable audio device includes: anacoustic transducer for providing audio playback of an audio signal to auser; an internal microphone acoustically coupled to an ear canal of auser, where the internal microphone generates an electrical signalresponsive to an acoustic signal incident at the internal microphone; aproximity sensor; and a control circuit coupled with the acoustictransducer, the internal microphone and the proximity sensor, thecontrol circuit configured to: determine a magnitude of an acoustictransfer function based on the electrical signal and the audio signal atone or more predetermined frequencies; calibrate the proximity sensor;detect a change in the wearable audio device from one of: an off-headstate to an on-head state, or the on-head state to the off-head stateusing both the calibrated proximity sensor and the magnitude of theacoustic transfer function; and adjust at least one function of thewearable audio device in response to detecting the change from theon-head state to the off-head state or detecting the change from theoff-head state to the on-head state.

In other particular aspects, a computer-implemented method of detectinga state of a wearable audio device on a user includes: detecting achange from one of: an on-head state to an off-head state, or theoff-head state to the on-head state, with a first sensor system, wherethe first sensor system comprises an internal microphone acousticallycoupled to an ear canal of a user, where the internal microphonegenerates an electrical signal responsive to an acoustical signalincident at the internal microphone, the detecting of the change fromthe on-head state to the off-head state or the off-head state to theon-head state comprising determining a magnitude of an acoustic transferfunction based on the electrical signal and the acoustical signal at oneor more predetermined frequencies; calibrating a second, distinct sensorsystem; detecting a change from the other one of: the off-head state tothe on-head state or the on-head state to the off-head state using thecalibrated second sensor system, where the second sensor systemcomprises a proximity sensor; and adjusting an operating state of atleast one function of the wearable audio device in response to detectingthe change from the on-head state to the off-head state or detecting thechange from the off-head state to the on-head state.

In additional particular aspects, a wearable audio device includes: anacoustic transducer for providing audio playback of an acoustical signalto a user; an internal microphone acoustically coupled to an ear canalof a user, where the internal microphone generates an electrical signalresponsive to an acoustic signal incident at the internal microphone;and a control circuit coupled with the acoustic transducer and theinternal microphone, the control circuit configured to: determine amagnitude of an acoustic transfer function based on the electricalsignal and the acoustical signal at one or more predeterminedfrequencies; pause the audio signal when a change from an on-head stateto an off-head state is detected; output an interrogation signal ornarrowband noise at the acoustic transducer while the audio signal ispaused; determine a magnitude of an acoustic transfer function based onthe electrical signal and the interrogation signal or narrowband noiseat one or more predetermined frequencies; and adjust at least onefunction of the wearable audio device in response to detecting one of: achange in the wearable audio device from the on-head state to theoff-head state or detecting a change from the off-head state to theon-head state.

Implementations may include one of the following features, or anycombination thereof.

In some cases, the control circuit is configured to determine themagnitude of the acoustic transfer function during the audio playback tothe user.

In particular aspects, the wearable audio device further includes anexternal microphone acoustically coupled to an environment external tothe wearable audio device, where the external microphone generates anelectrical signal responsive to an acoustic signal incident at theexternal microphone.

In certain implementations, the control circuit is further configuredto: measure a first transfer function based upon the audio signal playedback at the transducer and a control signal sent to the transducer forinitiating the audio playback; measure a second transfer function basedupon the audio signal played back at the transducer and the electricalsignal generated by the internal microphone; and based on a comparisonbetween the first transfer function and the second transfer function,detect a change in the wearable audio device from one of: an on-headstate to an off-head state, or the off-head state to the on-head state.

In some aspects, the control circuit is configured to determine thefirst transfer function and the second transfer function for each of aleft side of the wearable audio device and a right side of the wearableaudio device, where the change from the on-head state to the off-headstate or from the off-head state to the on-head state is detected onlywhen both the left side and the right side transfer functions are inagreement.

In particular cases, the proximity sensor includes a capacitiveproximity sensor or an infra-red (IR) sensor, and the proximity sensordetects proximity to a head of the user to indicate the change from theon-head state to the off-head state or from the off-head state to theon-head state.

In certain implementations, the acoustic transducer is configured tocontinuously provide the audio playback while the wearable audio deviceis in the on-head state.

In particular cases, the audio playback includes at least one of: anaudible feed or an interrogation signal.

In some aspects, the control circuit is further configured to pause theaudio playback in response to detecting the change from the on-headstate to the off-head state.

In particular implementations, the predetermined frequencies are below400 Hz.

In certain cases, the control circuit is further configured to: resumethe audio playback in response to the calibrated proximity sensordetecting the change from the off-head state to the on-head state; andre-calibrate the proximity sensor to the off-head state each time thechange from the on-head state to the off-head state is detected.

In some implementations, the control circuit includes an active noisereduction (ANR) circuit for generating a feedback noise cancellationsignal based on the electrical signal for output by the acoustictransducer.

In particular aspects, the function(s) include an audio playbackfunction, a power function, a capacitive touch interface function, anactive noise reduction (ANR) function, a controllable noise cancellation(CNC) function or a shutdown timer function.

In certain cases, the wearable audio device further includes a sensorsystem coupled with the control circuit for continuously operatingduring the on-head state, where the control circuit is furtherconfigured to: receive an indicator of an off-head detection event fromthe sensor system; and only in response to receiving the indicator ofthe off-head detection event, confirm the off-head detection event byusing the control circuit to determine a magnitude of an acoustictransfer function based on the electrical signal and the audio signal atone or more predetermined frequencies to detect a change from one of:the on-head state to the off-head state, or the off-head state to theon-head state.

In some aspects, the wearable audio device further includes a sensorsystem coupled with the control circuit, where the control circuit isfurther configured to: detect the change in the wearable audio devicefrom one of: the on-head state to the off-head state, or the off-headstate to the on-head state from the determined magnitude of the acoustictransfer function; and confirm the off-head state or the on-head stateusing the sensor system.

In particular implementations, the method further includes using anactive noise reduction (ANR) circuit to generate a feedback noisecancellation signal based on the electrical signal, for output by anacoustic transducer.

In certain cases, the method further includes receiving an indicator ofan off-head detection event from an additional sensor system; andinitiating the first sensor system to detect a change from the on-headstate to the off-head state in response to the indicator of the off-headdetection event from the additional sensor system.

In some aspects, the method further includes: continuously providingaudio playback to the user while the wearable audio device is in theon-head state, where the audio playback comprises an audible feed or aninterrogation signal detectable by the first sensor system; and pausingthe audio playback in response to the first sensor system detecting thechange from the on-head state to the off-head state.

In particular cases, the method further includes: resuming the audioplayback in response to the calibrated second sensor system detectingthe change from the off-head state to the on-head state; andre-calibrating the second sensor system to the off-head state each timethe change from the on-head state to the off-head state is detected.

In certain implementations, the wearable audio device further includesan external microphone acoustically coupled to an environment externalto the wearable audio device, where the external microphone generates anelectrical signal responsive to an acoustic signal incident at theexternal microphone.

In some cases, the method further includes: measuring a first transferfunction based upon the audio signal played back at the transducer and acontrol signal sent to the transducer for initiating the audio playback;measuring a second transfer function based upon the audio signal playedback at the transducer and the electrical signal generated by theinternal microphone; and based on a comparison between the firsttransfer function and the second transfer function, detecting a changein the wearable audio device from an on-head state to an off-head state.

In particular aspects, the method further includes determining the firsttransfer function and the second transfer function for each of a leftside of the wearable audio device and a right side of the wearable audiodevice, where the change from the on-head state to the off-head state isdetected only when both the left side and the right side transferfunctions are in agreement.

In certain cases, an active noise reduction (ANR) circuit or acontrolled noise cancelation (CNC) circuit includes a digital signalprocessor (DSP) chip for comparing acoustic signals received from afeedforward microphone and acoustic signals received from a feedbackmicrophone to detect the change from the on-head state to the off-headstate, where the control circuit is further configured to: awaken theDSP chip from a sleep mode in response to receiving the indicator of theoff-head detection event, or provide the audio playback only in responseto receiving the indicator of the off-head detection event.

In some aspects the wearable audio device does not have active noisereduction (ANR) capability or has ANR capability disengaged, and thecontrol circuit is configured to estimate the acoustic transfer functionat the one or more predetermined frequencies to detect the change in thewearable audio device from the on-head state to the off-head state.

In particular implementations, the magnitude of the acoustic transferfunction (G_(sd)) based on the electrical signal and the audio signal atone or more predetermined frequencies is calculated using four transferfunctions: O→D (T1), O→S (T2), A→D (T3) and A→S (T4), where O is theambient acoustic signal, A is the audio signal being played, S is thesystem (feedback) mic, and D is the driver signal, where G_(sd) iscalculated by comparing T3 and T4 to determine the off-head state.

Two or more features described in this disclosure, including thosedescribed in this summary section, may be combined to formimplementations not specifically described herein.

The details of one or more implementations are set forth in theaccompanying drawings and the description below. Other features, objectsand advantages will be apparent from the description and drawings, andfrom the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram depicting an example personal audio deviceaccording to various disclosed implementations.

FIG. 2 is a flowchart representation of an example of a method ofcontrolling a personal audio device 10 according to variousimplementations.

FIG. 3 a flowchart representation of an example of a method ofcontrolling a personal audio device 10 according to various additionalimplementations.

FIG. 4 is an example graphical depiction of a log scale for transferfunction (G_(sd)) calculation according to various implementations.

It is noted that the drawings of the various implementations are notnecessarily to scale. The drawings are intended to depict only typicalaspects of the disclosure, and therefore should not be considered aslimiting the scope of the implementations. In the drawings, likenumbering represents like elements between the drawings.

DETAILED DESCRIPTION

This disclosure is based, at least in part, on the realization that acontrol circuit can effectively detect the on/off head state of a userin a wearable audio device to provide for added functionality. Forexample, a control circuit can be configured to rely upon distincton-head state detection and off-head state detection mechanisms toeffectively detect don/doff events.

Commonly labeled components in the FIGURES are considered to besubstantially equivalent components for the purposes of illustration,and redundant discussion of those components is omitted for clarity.

In the examples of a personal audio device and a method of controlling apersonal audio device described below, certain terminology is used tobetter facilitate understanding of the examples. Reference is made toone or more “tones” where a tone means a substantially single frequencysignal. The tone may have a bandwidth beyond that of a single frequency,and/or may include a small frequency range that includes the value ofthe single frequency. For example, a 10 Hz tone may include a signalthat has frequency content in a range about 10 Hz.

It has become commonplace for those who either listen to electronicallyprovided audio (e.g., audio from an audio source such as a mobile phone,tablet, computer, CD player, radio or MP3 player), those who simply seekto be acoustically isolated from unwanted or possibly harmful sounds ina given environment, and those engaging in two-way communications toemploy personal audio devices to perform these functions. For those whoemploy headphones or headset forms of personal audio devices to listento electronically provided audio, it is commonplace for that audio to beprovided with at least two audio channels (e.g., stereo audio with leftand right channels) to be acoustically presented with separate earpiecesto each ear. Further, developments in digital signal processing (DSP)technology have enabled such provision of audio with various forms ofsurround sound involving multiple audio channels. For those simplyseeking to be acoustically isolated from unwanted or possibly harmfulsounds, it has become commonplace for acoustic isolation to be achievedthrough the use of active noise reduction (ANR) techniques based on theacoustic output of anti-noise sounds in addition to passive noisereduction (PNR) techniques based on sound absorbing and/or reflectingmaterials. Further, it is commonplace to combine ANR with other audiofunctions in headphones, headsets, earphones, earbuds and wirelessheadsets (also known as “earsets”). While the term ANR is used to referto acoustic output of anti-noise sounds, this term can also includecontrollable noise canceling (CNC), which permits control of the levelof anti-noise output, for example, by a user. In some examples, CNC canpermit a user to control the volume of audio output regardless of theambient acoustic volume.

Aspects and implementations disclosed herein may be applicable to a widevariety of wearable audio devices in various form factors, such aswatches, glasses, neck-worn speakers, shoulder-worn speakers, body-wornspeakers, etc. Unless specified otherwise, the term headphone, as usedin this document, includes various types of personal audio devices suchas around-the-ear, over-the-ear and in-ear headsets, earphones, earbuds,hearing aids, or other wireless-enabled audio devices structured to bepositioned near, around or within one or both ears of a user. Unlessspecified otherwise, the term wearable audio device, as used in thisdocument, includes headphones and various other types of personal audiodevices such as head, shoulder or body-worn acoustic devices thatinclude one or more acoustic drivers to produce sound without contactingthe ears of a user. Some particular aspects disclosed may beparticularly applicable to personal (wearable) audio devices such asheadphones or other head-mounted audio devices. It should be noted thatalthough specific implementations of personal audio devices primarilyserving the purpose of acoustically outputting audio are presented withsome degree of detail, such presentations of specific implementationsare intended to facilitate understanding through provision of examplesand should not be taken as limiting either the scope of disclosure orthe scope of claim coverage.

Aspects and implementations disclosed herein may be applicable topersonal audio devices that either do or do not support two-waycommunications, and either do or do not support active noise reduction(ANR). For personal audio devices that do support either two-waycommunications or ANR, it is intended that what is disclosed and claimedherein is applicable to a personal audio device incorporating one ormore microphones disposed on a portion of the personal audio device thatremains outside an ear when in use (e.g., feedforward microphones), on aportion that is inserted into a portion of an ear when in use (e.g.,feedback microphones), or disposed on both of such portions. Still otherimplementations of personal audio devices to which what is disclosed andwhat is claimed herein is applicable will be apparent to those skilledin the art.

FIG. 1 is a block diagram of an example of a personal audio device 10having two earpieces 12A and 12B, each configured to direct soundtowards an ear of a user. Reference numbers appended with an “A” or a“B” indicate a correspondence of the identified feature with aparticular one of the earpieces 12 (e.g., a left earpiece 12A and aright earpiece 12B). Each earpiece 12 includes a casing 14 that definesa cavity 16. In some examples, one or more internal microphones (innermicrophone) 18 may be disposed within cavity 16. In implementationswhere personal audio device 10 is ear-mountable, an ear coupling 20(e.g., an ear tip or ear cushion) attached to the casing 14 surrounds anopening to the cavity 16. A passage 22 is formed through the earcoupling 20 and communicates with the opening to the cavity 16. In someexamples, an outer microphone 24 is disposed on the casing in a mannerthat permits acoustic coupling to the environment external to thecasing.

In implementations that include ANR (which may include CNC), the innermicrophone 18 may be a feedback microphone and the outer microphone 24may be a feedforward microphone. In such implementations, each earphone12 includes an ANR circuit 26 that is in communication with the innerand outer microphones 18 and 24. The ANR circuit 26 receives an innersignal generated by the inner microphone 18 and an outer signalgenerated by the outer microphone 24 and performs an ANR process for thecorresponding earpiece 12. The process includes providing a signal to anelectroacoustic transducer (e.g., speaker) 28 disposed in the cavity 16to generate an anti-noise acoustic signal that reduces or substantiallyprevents sound from one or more acoustic noise sources that are externalto the earphone 12 from being heard by the user. As described herein, inaddition to providing an anti-noise acoustic signal, electroacoustictransducer 28 can utilize its sound-radiating surface for providing anaudio output for playback, e.g., for a continuous audio feed.

A control circuit 30 is in communication with the inner microphones 18,outer microphones 24, and electroacoustic transducers 28, and receivesthe inner and/or outer microphone signals. In certain examples, thecontrol circuit 30 includes a microcontroller or processor 35, includingfor example, a digital signal processor (DSP) and/or an ARM chip. Insome cases, the microcontroller/processor (or simply, processor) 35 caninclude multiple chipsets for performing distinct functions. Forexample, the processor 35 can include a DSP chip for performing musicand voice related functions, and a co-processor such as an ARM chip (orchipset) for performing sensor related functions.

The control circuit 30 can also include analog to digital converters forconverting the inner signals from the two inner microphones 18 and/orthe outer signals from the two outer microphones 24 to digital format.In response to the received inner and/or outer microphone signals, thecontrol circuit 30 (including processor 35) can take various actions.For example, audio playback may be initiated, paused or resumed, anotification to a user (e.g., wearer) may be provided or altered, and adevice in communication with the personal audio device may becontrolled. The personal audio device 10 also includes a power source32. The control circuit 30 and power source 32 may be in one or both ofthe earpieces 12 or may be in a separate housing in communication withthe earpieces 12. The personal audio device 10 may also include anetwork interface 34 to provide communication between the personal audiodevice 10 and one or more audio sources and other personal audiodevices. The network interface 34 may be wired (e.g., Ethernet) orwireless (e.g., employ a wireless communication protocol such as IEEE802.11, Bluetooth, Bluetooth Low Energy (BLE), or other local areanetwork (LAN) or personal area network (PAN) protocols).

Network interface 34 is shown in phantom, as portions of the interface34 may be located remotely from personal audio device 10. The networkinterface 34 can provide for communication between the personal audiodevice 10, audio sources and/or other networked (e.g., wireless) speakerpackages and/or other audio playback devices via one or morecommunications protocols. The network interface 34 may provide either orboth of a wireless interface and a wired interface. The wirelessinterface can allow the personal audio device 10 to communicatewirelessly with other devices in accordance with any communicationprotocol noted herein. In some particular cases, a wired interface canbe used to provide network interface functions via a wired (e.g.,Ethernet) connection.

In some cases, the network interface 34 may also include a network mediaprocessor for supporting, e.g., Apple AirPlay® (a proprietary protocolstack/suite developed by Apple Inc., with headquarters in Cupertino,Calif., that allows wireless streaming of audio, video, and photos,together with related metadata between devices) or other known wirelessstreaming services (e.g., an Internet music service such as: Pandora®, aradio station provided by Pandora Media, Inc. of Oakland, Calif., USA;Spotify®, provided by Spotify USA, Inc., of New York, N.Y., USA); orvTuner®, provided by vTuner.com of New York, N.Y., USA); andnetwork-attached storage (NAS) devices). For example, if a user connectsan AirPlay® enabled device, such as an iPhone or iPad device, to thenetwork, the user can then stream music to the network connected audioplayback devices via Apple AirPlay®. Notably, the audio playback devicecan support audio-streaming via AirPlay® and/or DLNA's UPnP protocols,and all integrated within one device. Other digital audio coming fromnetwork packets may come straight from the network media processorthrough (e.g., through a USB bridge) to the control circuit 30. As notedherein, in some cases, control circuit 30 can include a processor and/ormicrocontroller (simply, “processor” 35), which can include decoders,DSP hardware/software, ARM processor hardware/software, etc. for playingback (rendering) audio content at electroacoustic transducers 28. Insome cases, network interface 34 can also include Bluetooth circuitryfor Bluetooth applications (e.g., for wireless communication with aBluetooth enabled audio source such as a smartphone or tablet). Inoperation, streamed data can pass from the network interface 34 to thecontrol circuit 30, including the processor or microcontroller (e.g.,processor 35). The control circuit 30 can execute instructions (e.g.,for performing, among other things, digital signal processing, decoding,and equalization functions), including instructions stored in acorresponding memory (which may be internal to control circuit 30 oraccessible via network interface 34 or other network connection (e.g.,cloud-based connection). The control circuit 30 may be implemented as achipset of chips that include separate and multiple analog and digitalprocessors. The control circuit 30 may provide, for example, forcoordination of other components of the personal audio device 10, suchas control of user interfaces (not shown) and applications run by thepersonal audio device 10.

In addition to a processor and/or microcontroller, control circuit 30can also include one or more digital-to-analog (D/A) converters forconverting the digital audio signal to an analog audio signal. Thisaudio hardware can also include one or more amplifiers which provideamplified analog audio signals to the electroacoustic transducer(s) 28,which each include a sound-radiating surface for providing an audiooutput for playback. In addition, the audio hardware may includecircuitry for processing analog input signals to provide digital audiosignals for sharing with other devices.

The memory in control circuit 30 can include, for example, flash memoryand/or non-volatile random access memory (NVRAM). In someimplementations, instructions (e.g., software) are stored in aninformation carrier. The instructions, when executed by one or moreprocessing devices (e.g., the processor or microcontroller in controlcircuit 30), perform one or more processes, such as those describedelsewhere herein. The instructions can also be stored by one or morestorage devices, such as one or more (e.g. non-transitory) computer- ormachine-readable mediums (for example, the memory, or memory on theprocessor/microcontroller). As described herein, the control circuit 30(e.g., memory, or memory on the processor/microcontroller) can include acontrol system including instructions for controlling directional audioselection functions according to various particular implementations. Itis understood that portions of the control circuit 30 (e.g.,instructions) could also be stored in a remote location or in adistributed location, and could be fetched or otherwise obtained by thecontrol circuit 30 (e.g., via any communications protocol describedherein) for execution. The instructions may include instructions forcontrolling device functions based upon detected don/doff events (i.e.,the software modules include logic for processing inputs from a sensorsystem to manage audio functions), as well as digital signal processingand equalization. Additional details may be found in U.S. PatentApplication Publication 20140277644, U.S. Patent Application Publication20170098466, and U.S. Patent Application Publication 20140277639, thedisclosures of which are incorporated herein by reference in theirentirety.

Personal audio device 10 can also include a sensor system 36 coupledwith control circuit 30 for detecting one or more conditions of theenvironment proximate personal audio device 10. Sensor system 36 caninclude inner microphones 18 and/or outer microphones 24, sensors fordetecting inertial conditions at the personal audio device and/orsensors for detecting conditions of the environment proximate personalaudio device 10 as described herein. Sensor system 36 can also includeone or more proximity sensors, such as a capacitive proximity sensor oran infra-red (IR) sensor, and/or one or more optical sensors.

The sensors may be on-board the personal audio device 10, or may beremote or otherwise wirelessly (or hard-wired) connected to the personalaudio device 10. As described further herein, sensor system 36 caninclude a plurality of distinct sensor types for detecting proximityinformation, inertial information, environmental information, orcommands at the personal audio device 10. In particular implementations,sensor system 36 can enable detection of user movement, includingmovement of a user's head or other body part(s). Portions of sensorsystem 36 may incorporate one or more movement sensors, such asaccelerometers, gyroscopes and/or magnetometers and/or a single inertialmeasurement unit (IMU) having three-dimensional (3D) accelerometers,gyroscopes and a magnetometer.

In various implementations, the sensor system 36 can be located at thepersonal audio device 10, e.g., where a proximity sensor is physicallyhoused in the personal audio device 10. In some examples, the sensorsystem 36 is configured to detect a change in the position of thepersonal audio device 10 relative to the user's head. Data indicatingthe change in the position of the personal audio device 10 can be usedto trigger a command function, such as activating an operating mode ofthe personal audio device 10, modifying playback of audio at thepersonal audio device 10, or controlling a power function of thepersonal audio device 10.

The sensor system 36 can also include one or more interface(s) forreceiving commands at the personal audio device 10. For example, sensorsystem 36 can include an interface permitting a user to initiatefunctions of the personal audio device 10. In a particular exampleimplementation, the sensor system 36 can include, or be coupled with, acapacitive touch interface for receiving tactile commands on thepersonal audio device 10.

In other implementations, as illustrated in the phantom depiction inFIG. 1, one or more portions of the sensor system 36 can be located atanother device capable of indicating movement and/or inertialinformation about the user of the personal audio device 10. For example,in some cases, the sensor system 36 can include an IMU physically housedin a hand-held device such as a smart device (e.g., smart phone, tablet,etc.) a pointer, or in another wearable audio device. In particularexample implementations, at least one of the sensors in the sensorsystem 36 can be housed in a wearable audio device distinct from thepersonal audio device 10, such as where personal audio device 10includes headphones and an IMU is located in a pair of glasses, a watchor other wearable electronic device.

Methods have been developed for determining the operating state of anearpiece as being on head or off head. Certain methods for determiningthe operating state for a personal audio device having ANR capability byanalyzing the inner and/or outer signals are described, for example, inU.S. Pat. No. 8,238,567, “Personal Acoustic Device PositionDetermination,” U.S. Pat. No. 8,699,719, “Personal Acoustic DevicePosition Determination,” U.S. Pat. No. 9,860,626, “On/Off Head Detectionof Personal Acoustic Device,” and U.S. Pat. No. 9,838,812, “On/Off HeadDetection of Personal Acoustic Device using an Earpiece Microphone”, thedisclosures of which are incorporated herein by reference in theirentirety.

Knowledge of a change in the operating state from on head to off head,or from off head to on head, can be applied for different purposes. Forexample, features of the personal audio device may be enabled ordisabled according to a change of operating state. In a specificexample, upon determining that at least one of the earpieces of apersonal audio device has been removed from a user's ear to become offhead, power supplied to the device may be reduced or terminated. Powercontrol executed in this manner can result in longer durations betweencharging of one or more batteries used to power the device and canincrease battery lifetime. Optionally, a determination that one or moreearpieces have been returned to the user's ear can be used to resume orincrease the power supplied to the device. In other cases, one or moreinterfaces can be controlled using knowledge of the on/off head state,e.g., a capacitive touch interface can be disabled when the off-headstate is detected. Audio playback can also be controlled using knowledgeof the on/off head state, e.g., to pause or resume playback. Noisecancellation/reduction can also be controlled using knowledge of theon/off head state, e.g., to adjust the controllable noise cancellation(CNC) level of the device.

With continuing reference to FIG. 1, in one example implementation, thecontrol circuit 30 is in communication with the inner microphones 18 andreceives the two inner signals. Alternatively, the control circuit 30may be in communication with the outer microphones 24 and receive thetwo outer signals. In another alternative, the control circuit 30 may bein communication with both the inner microphones 18 and outermicrophones 24, and receives the two inner and two outer signals. Itshould be noted that in some implementations, there may be multipleinner and/or outer microphones in each earpiece 12. As noted herein, thecontrol circuit 30 can include a microcontroller or processor having aDSP and the inner signals from the two inner microphones 18 and/or theouter signals from the two outer microphones 24 are converted to digitalformat by analog to digital converters. In response to the receivedinner and/or outer signals, the control circuit 30 can take variousactions. For example, the power supplied to the personal audio device 10may be reduced upon a determination that one or both earpieces 12 areoff head. In another example, full power may be returned to the device10 in response to a determination that at least one earpiece becomes onhead. Other aspects of the personal audio device 10 may be modified orcontrolled in response to determining that a change in the operatingstate of the earpiece 12 has occurred. For example, ANR functionalitymay be enabled or disabled, audio playback may be initiated, paused orresumed, a notification to a wearer may be altered, and a device incommunication with the personal audio device may be controlled. Asillustrated, the control circuit 30 generates a signal that is used tocontrol a power source 32 for the device 10. The control circuit 30 andpower source 32 may be in one or both of the earpieces 12 or may be in aseparate housing in communication with the earpieces 12.

When an earpiece 12 is positioned on head, the ear coupling 20 engagesportions of the ear and/or portions of the user's head adjacent to theear, and the passage 22 is positioned to face the entrance to the earcanal. As a result, the cavity 16 and the passage 22 are acousticallycoupled to the ear canal. At least some degree of acoustic seal isformed between the ear coupling 20 and the portions of the ear and/orthe head of the user that the ear coupling 20 engages. This acousticseal at least partially acoustically isolates the now acousticallycoupled cavity 16, passage 22 and ear canal from the environmentexternal to the casing 14 and the user's head. This enables the casing14, the ear coupling 20 and portions of the ear and/or the user's headto cooperate to provide some degree of PNR. Consequently, sound emittedfrom external acoustic noise sources is attenuated to at least somedegree before reaching the cavity 16, the passage 22 and the ear canal.Sound generated by each speaker 28 propagates within the cavity 16 andpassage 22 of the earpiece 12 and the ear canal of the user, and mayreflect from surfaces of the casing 14, ear coupling 20 and ear canal.This sound can be sensed by the inner microphone 18. Thus the innersignal is responsive to the sound generated by the speaker 28.

The outer signals generated by the outer microphones 24 may be used in acomplementary manner. When the earpiece 12 is positioned on head, thecavity 16 and the passage 22 are at least partially acousticallyisolated from the external environment due to the acoustic seal formedbetween the ear coupling 20 and the portions of the ear and/or the headof the user. Thus, sound emitted from the speakers 28 is attenuatedbefore reaching the outer microphones 24. Consequently, the outersignals are generally substantially non-responsive to the soundgenerated by the speakers 28 while the earpiece 12 is in an on-headoperating state.

When the earpiece 12 is removed from the user so that it is off head andthe ear coupling 20 is therefore disengaged from the user's head, thecavity 16 and the passage 22 are acoustically coupled to the environmentexternal to the casing 14. This allows the sound from the speaker 28 topropagate into the external environment. As a result, the transferfunction defined by the outer signal of the outer microphone 24 relativeto the signal driving the speaker 28 generally differs for the twooperating states. More particularly, the magnitude and phasecharacteristics of the transfer function for the on head operating stateare different from the magnitude and phase characteristics of thetransfer function for the off-head operating state.

FIG. 2 is a flowchart representation of an example of a method ofcontrolling a personal audio device 10 according to variousimplementations. Processes described with respect to the method can beperformed by one or more components in the personal audio device 10(FIG. 1), in particular, by the control circuit 30. It is understoodthat the control circuit 30 can include multiple circuits, or chips,configured to perform particular functions described herein. The controlcircuit 30 is configured to perform processes to control the personalaudio device 10, e.g., to control operations in response to detecting anon-head state and/or off-head state event.

As described herein, the personal audio device 10 includes internalmicrophones 18 that are acoustically coupled to the user's ear canalwhen the personal audio device 10 is in the on-head state. Each internalmicrophone 18 generates an electrical signal responsive to an acousticalsignal from the transducer 28 incident at the internal microphone 18. Ina first process (process 210), the control circuit 30 determines amagnitude of an acoustic transfer function (G_(sd)) based on theelectrical signal generated by the internal microphone 18 and theacoustical signal received at the internal microphone 18 at one or morepredetermined frequencies, for example frequencies below 400 Hz. Thatis, as described herein, the control circuit 30 is configured toestimate the “acoustic transfer function (G_(sd))”, which is a quantitythat is calculated based upon measured transfer function components. Ina laboratory setting, this acoustic transfer function (G_(sd)) can bemeasured by computing a transfer function between the driver signal(voltage) and feedback microphone signal (voltage) in the absence ofnoise or other sound, that is, without ANR functionality running.However, in practice, it is difficult to directly measure the acoustictransfer function (G_(sd)) in a wearable audio device because ANRfunctionality is often employed. As such, the acoustic transfer function(G_(sd)) described herein is noted as an estimated function that isbased upon other measured transfer function components. This “acoustictransfer function (G_(sd))” differs from measured transfer functionvalues, and is denoted as such herein.

With continuing reference to FIG. 2, if the magnitude of the acoustictransfer function does not exceed a threshold value, the control circuit30 periodically recalculates the acoustic transfer function, asindicated by the loop in FIG. 2 (No to decision 220). This acoustictransfer function can be continuously calculated, or triggered by anevent, e.g., a sensor event such as detection of movement of thepersonal audio device 10 by a sensor such as an infra-red sensor orcapacitive proximity sensor. The threshold value is established usingcalculations of voltage differentials when the personal audio device 10is off-head, and on-head, respectively, e.g., between the driver signaland feedback microphone signal(s). When the magnitude of this acoustictransfer function (G_(sd)) is below a threshold value (Yes to decision220), the control circuit 30 determines that the personal audio device10 has changed from an on-head state to an off-head state (process 230).In this sense, the transducer 28 and the microphone 18 provide a firstsensor system for the control circuit 30 to detect the change from theon-head state to the off-head state.

In various implementations, the control circuit 30 is configured todetermine the magnitude of the acoustic transfer function (G_(sd))during the audio playback to the user. As described herein, the audioplayback can include an audible feed (e.g., music, a podcast, an audiblebook, etc.), or an interrogation signal (e.g., an audible tone, amarginally audible tone or inaudible tone, which may be at a singlefrequency) detectable by the first sensor system (e.g., microphone 18).According to some implementations, to aid in detecting the change fromon-head state to off-head state, the control circuit 30 continuouslyprovides the audio playback to the user while the personal audio device10 is determined to be in the on-head state. That is, even when the useris not electively playing audio at the personal audio device 10, thecontrol circuit 30 is configured to output an interrogation signal(e.g., inaudible tone, marginally audible tone, or an audible tone) atthe transducer 28 to aid in detecting the change from the on-head stateto the off-head state. In some particular implementations, theinterrogation signal in the audio playback is output to coincide infrequency with the range of the computed acoustic transfer function(G_(sd)).

In particular implementations, determining the magnitude of the acoustictransfer function (G_(sd)) to determine the off-head state includescalculating multiple acoustic transfer functions, as measured fromsignals received and/or sent by the control circuit 30. In a particularexample, the control circuit 30 is configured to determine the magnitudeof the acoustic transfer function (G_(sd)) based upon the electricalsignal and the received acoustical signal by:

A) measuring a first transfer function based upon the audio signalplayed back at the transducer 28 and a control signal sent (from thecontrol circuit 30) to the transducer 28 for initiating the audioplayback;

B) measuring a second transfer function based upon the audio signalplayed back at the transducer 28 and the electrical signal generated bythe internal microphone 18; and

C) detect the change in the personal audio device 10 from the on-headstate to the off-head state based upon a comparison between the firsttransfer function and the second transfer function. In variousimplementations, the comparison between the first transfer function andthe second transfer function generates a ratio, or a difference (after alog transform). This ratio is an estimate of the acoustic transferfunction (G_(sd)) value, which can be compared to the ratio of measuredtransfer functions that constitute the threshold in order to detect thechange from on-head to off-head state.

In particular implementations, the control circuit 30 is configured todetermine the first acoustic transfer function and the second acoustictransfer function for each of the left side and the right side of thepersonal audio device 10. In these cases, the control circuit 30 onlydetermines that the audio device has changed from the on-head state tothe off-head state when both the left and right side acoustic transferfunctions are in agreement, that is, both indicate the change from theon-head state to the off-head state.

The approaches for detecting change from the on-head state to theoff-head state can be useful in conserving power resources for the audiodevice 10. That is, these approaches can rely upon a triggering eventfrom the second sensor system (e.g., proximity sensor or an additionalsensor) to initiate the process of determining the magnitude of theacoustic transfer function (G_(sd)) and determining an on-head tooff-head event. In these cases, the computationally intensive processesof calculating the magnitude of the acoustic transfer function can beinitiated only after the second sensor system (or another sensor system)indicates that movement has occurred.

With continuing reference to FIG. 2, the control circuit 30 is furtherconfigured, after determining that the audio device 10 has changed statefrom on head to off head (process 230), to calibrate a second, distinctsensor system to the off-head state (process 240). This second sensorsystem can be located in sensor system 36, and can be physically locatedat the personal audio device 10. In some cases, the second sensor systemincludes a proximity sensor such as a capacitive proximity sensor or aninfra-red (IR) sensor. This proximity sensor can be located internal tothe casing 14, or can be otherwise directed toward the head or body ofthe user, and is configured to detect proximity of the personal audiodevice 10, e.g., the earpiece 12, to an object. In some cases, eachearpiece 12 has a proximity sensor to enable independent proximitydetection for both sides of the personal audio device 10. However, otherimplementations of the personal audio device 10 include a proximitysensor proximate only one of the earpieces 12.

As noted herein, the second sensor system can be calibrated in order todetect a change in the personal audio device 10 from the off-head stateto the on-head state. In some cases, the control circuit 30 calibratesthe second sensor system to account for environmental variations in useand/or distinctions in operating modes and/or capabilities of thepersonal audio device 10. For example, the second sensor system can becalibrated to recognize separation (or lack of proximity) from theuser's head, ear or body when the first sensor system detects that thepersonal audio device 10 is in the off-head state.

In particular cases, the control circuit 30 performs the calibration bymeasuring a value of the signal received from the second sensor systemwhen the first sensor system detects that the person audio device 10 isin the off-head state. The control circuit 30 then identifies thissignal value as the baseline value. Using this baseline value, thecontrol circuit 30 can dynamically set a threshold for on-headdetection, for example, by assigning a threshold to a signal value thatis one or more standard deviations above the baseline value (e.g., threeor four standard deviations above the baseline). In variousimplementations, in order to detect the change from off-head to on-headstate, the control circuit 30 must receive a subsequent signal from thesecond sensor system that has a value exceeding the threshold value. Inparticular cases, this on-head detection threshold can be re-calculatedeach time that the first sensor system detects that the personal audiodevice 10 changes from the on-head state to the off-head state (e.g.,within a power cycle). However, in cases where the control circuit 30recognizes that the detected signal value is significantly greater thanthe established threshold (e.g., one or more additional standarddeviations above the baseline as compared with the threshold), thecontrol circuit 30 can be configured to prevent additional calibration,e.g., within that power cycle. That is, where the detected signal valuefrom the second sensor system (indicating the donning event) issignificantly greater than the threshold value, the control circuit 30does not perform additional calibration/calculation for the nextdetected transition from the on-head state to the off-head state withinthat power cycle.

Additionally, or alternatively, in cases where the control circuit 30recognizes that the detected signal value is significantly greater thanthe established threshold (e.g., one or more additional standarddeviations above the baseline as compared with the threshold) and/or theearpiece 12 is determined to have a poor seal on the user's body, thecontrol circuit 30 can be configured to use only the second sensorsystem to detect changes from on-head to off-head and/or off-head toon-head state(s). As noted herein, there are circumstances where thedetected signal value from the second sensor system is significantlyhigher than the established threshold so as to clearly indicate a changein state, e.g., from off-head to on-head. In additional cases, themargin in the acoustic transfer function (G_(sd)) value between theon-head state and the off-head state may be too small (e.g., below athreshold) to reliably indicate a change in state, e.g., from theon-head state to the off-head state. This small margin in the acoustictransfer function (G_(sd)) values can indicate that the earpiece 12 hasa poor seal on the user's body (e.g., ear, head, etc.), such that a toneor other audio playback will not be effectively detected for thepurposes of don/doff detection. In one or both such cases (which are notmutually exclusive), the control circuit 30 can be configured to relysolely on the second sensor system signals to detect on-off head and/oroff-on head state changes, e.g., within that power cycle.

The calibrated second sensor system (e.g., proximity sensor) can be usedto detect a change in the personal audio device 10 from the off-headstate to the on-head state (process 250). In particular cases, thecalibrated sensor system can be used to detect that the user has placedthe personal audio device 10 back on his/her body, e.g., on his/herears. Where the calibrated sensor system includes one or more proximitysensors, the proximity sensor(s) can send a signal to the controlcircuit 30 indicating that one or both earpieces 12 are in contact with,or proximate to, the body of the user. In some cases, the proximitysensor is calibrated to send a proximity signal when detecting an objectwithin a threshold distance. Once the personal audio device 10 is placedwithin that threshold distance from the user, the proximity sensor sendsthe proximity sensor signal to the control circuit 30 to indicate atrigger event. In various implementations, this approach can conservepower (e.g., batter power from the power source 32) to extend the lifeof the personal audio device 10.

In response to determining that the personal audio device 10 has had astate change, either from on-head state to off-head state, or fromoff-head state to on-head state, in some examples, the control circuit30 is further configured to adjust at least one function of the personalaudio device 10 (process 260). Function adjustments can beuser-configurable (i.e., adjustable via a menu interface on an app incommunication with the personal audio device 10) and/or programmed intocontrol circuit 30 such that some functions are controlled by on-to-offhead detection and a possibly distinct group of functions are controlledby off-to-on head detection. In some cases, the control circuit 30 isconfigured to adjust functions including one or more of: an audioplayback function, a power function, a capacitive touch interfacefunction, an active noise reduction (ANR) function, a controllable noisecancellation (CNC) function or a shutdown timer function.

For example, according to some implementations, the control circuit 30is configured to pause the audio playback (e.g., user-selected playback,narrowband noise, interrogation signal, etc.) in response to detectingthe change from the on-head state to the off-head state. In someimplementations, the control circuit 30 is configured to resume theaudio playback (e.g., playback, narrowband noise, interrogation signal,etc.) that was previously paused in response to the calibrated proximitysensor detecting the change from the off-head state to the on-headstate. Additionally, ANR and CNC functions can be disabled or powereddown in response to determining that the personal audio device 10 haschanged from on-head to off-head state. In other cases, the controlcircuit 30 can initiate a shutdown timer in response to detecting thechange from the on-head state to the off-head state, e.g., to power downthe personal audio device 10 after a threshold period has elapsed. Incertain cases, control circuit 30 need not adjust a function of thepersonal audio device 10 in response to detecting a state change, andcan simply log or otherwise store data indicating the state change.

In various implementations, processes 210-250 (as well as process 260),can be run continuously, that is, each time that the user dons/doffs thepersonal audio device 10. In particular cases, each time the personalaudio device 10 changes state from the on-head state to the off-headstate, the control circuit 30 is configured to re-calibrate the secondsensor system (e.g., proximity sensor). In still further particularcases, the control circuit 10 is configured to re-calibrate the secondsensor system each time the control circuit 10 detects an environmentalchange (e.g., using data from sensor system 36 such as GPS data,temperature or humidity data, weather data, etc.). In additional examplecases, this iterative re-calibration process can be performed only foreach instance when the personal audio device 10 is used, e.g., only onceper power cycle for the personal audio device 10. In theseimplementations, on-off head state detection can be performed using thefirst sensor system once per power cycle. In these cases, within a givenpower cycle, additional on-off head state events can be detectedexclusively by the second sensor system (e.g., proximity sensor) oncethe first sensor system has been calibrated for the user. This processcan reduce power and/or processing load for the control circuit 30relative to re-calibrating the second sensor system each time theon-head to off-head state detection is triggered.

In some cases, with continuing reference to FIG. 1 and FIG. 2, thesensor system 36 can include an additional sensor for continuouslyoperating during the on-head state. This additional sensor can be usedto supplement state detection performed by the proximity sensor and theinternal microphone 18/transducer 28, described with reference toprocesses 210-260. The additional sensor can include any sensorconfigured to detect an event, such as a movement of the personal audiodevice 10. In one example, the additional sensor includes an IMU. Invarious implementations, the control circuit 30 is further configured toreceive an indicator of an off-head detection event from the additionalsensor, which is shown as an optional preliminary process (process 205)in FIG. 2. In some cases, this indicator is a sensor signal thatindicates the personal audio device 10 has moved (e.g., in terms oftranslation, rotation, etc.) a threshold distance or in a manner thatcorresponds with a change from on-head state to off-head state. In othercases, the additional sensor includes an optical sensor configured todetect movement of the personal audio device 10 and transmit a signal tothe control circuit 30 indicating that the personal audio device 10(e.g., an earpiece 12) has meets or exceeds a state detection threshold.

In particular implementations, the additional sensor can be used as aninitial screening sensor to detect the change from the on-head state tothe off-head state. In these cases, the control circuit 30 receives theindicator of an off-head detection event from the additional sensor, andin response to receiving that indicator, confirms the off-head detectionevent by determining a magnitude of the acoustic transfer function(G_(sd)) based on the electrical signal and the audio signal at one ormore predetermined frequencies. In the case that the magnitude of theacoustic transfer function (G_(sd)) meets or exceeds the on-to-off headstate detection threshold, the control circuit 30 does not indicate achange in the state from on-head to off-head (No to decision 220).However, if the magnitude of the acoustic transfer function (G_(sd)) isbelow the on-to-off head state detection threshold (Yes to decision220), the control circuit 30 indicates the change in state from on-headto off-head, and may take additional action such as adjustingfunction(s) of the personal audio device 10.

In still other implementations, the additional sensor can be used as anon-head to off-head state verification system. In these cases, theadditional sensor acts as the second level sensor modality to determinethat the personal audio device 10 has changed state from on-head tooff-head. With reference to FIG. 2, in these cases, after the controlcircuit 30 determines that the audio device is off-head (process 230),the additional sensor is used to confirm the off-head state, shown as anoptional process (process 235). This confirmation can be performedaccording to any approach described herein, e.g., using an IMU, opticalsensor or other sensor system to detect movement that meets or exceeds athreshold corresponding with an off-head event. In theseimplementations, the control circuit 30 may only take action (e.g.,adjust functions of the audio device, process 260; or indicate/log anoff-head event) in response to receiving the confirmation from theadditional sensor.

As described herein, in some example implementations, the personal audiodevice 10 can include one or more ANR circuits 26 (FIG. 1) forperforming noise cancelling or noise reduction functions. The ANRcircuit 26 can rely upon the external microphone(s) 24 to detect (andultimately control) an amount of ambient noise that is played back tothe user. As noted herein, the external microphone 24 is acousticallycoupled to the environment external to the personal audio device 10. Invarious implementations, this external microphone 24 generates anelectrical signal responsive to an acoustic signal (e.g., any ambientacoustic signal) incident at the external microphone 24.

This ANR functionality may provide additional modalities for detectingthe on/off state of the personal audio device 10. For example, the ANRcircuit 26 can generate a feedback noise cancellation signal based onthe electrical signal generated by the internal microphone 18. Thisfeedback noise cancellation signal is output by the transducer 28 tocancel or otherwise reduce ambient noise. In implementations, the ANRcircuit 26 (which can include CNC functionality) includes a DSP chip forcomparing acoustic signals received from the outer (feedforward)microphone 24 and acoustic signals received from the inner (feedback)microphone 18 to detect the change from the on-head state to theoff-head state. In additional cases, as noted herein, the processor 35includes an audio DSP chip or ARM chip for comparing acoustic signalsreceived from the outer (feedforward) microphone 24 and acoustic signalsreceived from the inner (feedback) microphone 18 to detect the changefrom the on-head state to the off-head state. In either case, thecontrol circuit 30 is configured to: a) awaken the DSP chip from a sleepmode in response to receiving the indicator of the off-head detectionevent, or b) provide the audio playback only in response to receivingthe indicator of the off-head detection event.

In still other cases, where the personal audio device 10 does not haveANR functionality, or where ANR functionality is disengaged (e.g., byuser command or settings), the control circuit 30 can be configured toestimate the acoustic transfer function (G_(sd)) at one or morepredetermined frequencies to detect the change from on-head to off-headstate. In practice, this process can involve calculating or estimatingvalues for one or more acoustic transfer function components to G_(sd).For example, G_(sd) can be calculated according to: O→D (T1); O→S (T2);A→D (T3); and A→S (T4), where O is the ambient acoustic signal detectedby an external microphone (e.g., the outer microphone 24 or any externalmicrophone on the personal audio device 10), A is the audio signaloutput at the transducer 28, S is the system (feedback) microphone 18signal, and D is the driver signal sent to the transducer 28. In somecases, as noted herein, G_(sd) is calculated by comparing T3 and T4 todetermine off-head state. However, in other implementations (e.g.,without use of ANR), T4 is calculated and compared with the thresholdestablished by G_(sd) measurements

FIG. 3 is a flowchart representation of an example of an additionalmethod of controlling a personal audio device 10 that is playing backaudio according to various implementations. In these implementations,the personal audio device 10 may not rely upon sensors from the sensorsystem 36 to detect the on/off state of the personal audio device 10.That is, the proximity sensor and/or additional sensors described hereinmay not be employed to detect the on/off state of the personal audiodevice 10 in these implementations, and instead, playback signals can beused to detect and verify on/off state. FIG. 3 is referred tosimultaneously with FIG. 1, and illustrates processes performed bycontrol circuit 30 according to implementations.

The method can include detecting a change from an on-head state to anoff-head state for the personal audio device 10 that is playing backaudio (e.g., user-selected audio such as music, an audio book, etc.). Invarious implementations, this process includes determining a magnitudeof the acoustic transfer function (G_(sd)) based on the electricalsignal and the audio signal at one or more predetermined frequencies todetect a change in the personal audio device 10 from an on-head state toan off-head state, as described with respect to processes 210-230 inFIG. 2. These similar processes are shown in FIG. 3 as processes310-330. In response to detecting the change from on-head state tooff-head state, the control circuit 30 pauses the audio signal (process340), and outputs an interrogation signal or narrowband noise at thetransducer 28 (process 350) while the audio signal is paused. While theinterrogation signal or narrowband noise is playing, the control circuit30 then determines a magnitude of an acoustic transfer function based onthe electrical signal and the interrogation signal or narrowband noiseat one or more predetermined frequencies to detect a change from theoff-head state to the on-head state (process 360). As similarlydescribed with respect to processes 220 and 230, the control circuit 30is configured to compare the acoustic transfer function magnitude with athreshold (as determined by measured transfer function values), andeither repeat the calculation of the acoustic transfer function (No todecision 370) or determine that personal audio device 10 has changedstate from off-head to on-head (Yes to decision 380). In response todetecting either the change from on-head to off-head and/or off-head toon-head, the control circuit 30 can adjust at least one function of theaudio device 10 (process 390), as described herein.

FIG. 4 shows an example graphical depiction of G_(sd) calculations forthe personal audio device 10. In this example, dbV/V is plotted againstfrequency (Hertz), and estimates (calculations) of G_(sd) values areplotted for several use scenarios. This depiction illustrates the rangeof frequencies over which G_(sd) is substantially different in theon-head state as compared with the off-head state, e.g., as shown in thegap between the On-head plot (plot #1) and off-head plots (plots #2-4).The interrogation signal(s) and acoustic transfer function calculationsdescribed according to various implementations target this range offrequencies in order to effectively determine don/doff events. That is,in various implementations, the control circuit 30 is programmed tocalculate acoustic transfer functions across a range of knownfrequencies where on-head state and off-head state can be detected.

As noted herein, conventional systems and approaches fail to effectivelydetect don/doff events in personal audio devices. For example,conventional systems and approaches may compute and make a decisionbased upon a direct (measured) transfer function between microphonesignals, rather than estimating the acoustic transfer function (G_(sd))calculation as described with reference to various implementations.Additionally, these conventional systems and approaches do not usemicrophone-based approaches to calibrate other sensors to detectdon/doff events.

In contrast to conventional systems and approaches noted herein, theaudio device 10 disclosed according to various implementations canenable reliable detection of on/off state events. Various approachesemploy a dual-sensor approach that verifies a first sensor determinationwith a second, distinct sensor determination. In additionalimplementations, verification is performed by estimating acoustictransfer function values as one modality for checking don/doff events.The approaches described herein can aid in reducing power consumptionand false triggers that are prevalent in some conventional systems.Additionally, approaches described herein can improve the userexperience relative to conventional systems, e.g., by smoothing thetransitions from on-state to off-state, and vice versa.

The method(s) described include determining an operating state of thepersonal audio device 10 based on a characteristic of the acoustictransfer function. By way of an example, the characteristic can be amagnitude of the acoustic transfer function at one or more predeterminedfrequencies such as the frequency or frequencies of the secondelectrical signal. Alternatively, the characteristic of the acoustictransfer function may be a power spectrum over a predefined frequencyrange. For example, the power spectrum characteristic may be useful whenthe second electrical signal is an audio content signal. Determining thepower spectra may include converting the first and second electricalsignals into the frequency domain and performing additional processing.In another alternative, the characteristic can be a phase of theacoustic transfer function at one or more predetermined frequencies. Inone non-limiting example, a predetermined frequency can be approximately1.5 KHz corresponding to a significant separation between the phases atthat frequency for the on head operating state with respect to the offhead operating state.

The method(s) described herein may be applied to both earpieces of apersonal audio device. If it is determined that only one of theearpieces changes its operating state, one set of operations of thepersonal audio device may be changed. In contrast, if it is determinedthat both earpieces have changed state, a different set of operationsmay be modified. For example, if it is determined that only one earpiecebeen changed from an on head to off head operating state, audio playbackof the personal acoustic device may be paused. Audio playback may beresumed if it is determined that the earpiece changes back to an on headoperating state. In another example, if it is determined that bothearpieces have changed from an on head to off head operating state, thepersonal audio device may be put into a low power state to conserveelectrical power. Conversely, if both earpieces are then determined tochange to an on head operating state, the personal audio device can bechanged to a normal operational power mode.

The particular characteristic of the acoustic transfer function employedin the methods described above, and whether an inner microphone signal,and outer microphone signal, or both are used, may be based on the typeof headset. For example, a headset with around-ear earpieces may utilizethe method based on the magnitude characteristic of the acoustictransfer function for determining the operating state and an in-earheadset may utilize the method based on the phase characteristic of theacoustic transfer function. In some implementations the method is basedon both magnitude and phase characteristics of the acoustic transferfunction. Moreover, the method can be used in combination with one ormore other methods for determining the operating state of the earpieceor to confirm a determination made by a different method of determiningthe operating state. For example, the above methods could be used toconfirm a determination made from a proximity sensor (e.g., acapacitance sensor) and/or a motion sensor (e.g., accelerometer) sensingthat the earpiece is off head.

In various examples described above, a feedback (or internal) and/orfeedforward (or external) microphone is used; however, it should berecognized that the microphone(s) do not have to be part of an ANRsystem and that one or more independent microphones may instead be used.

The functionality described herein, or portions thereof, and its variousmodifications (hereinafter “the functions”) can be implemented, at leastin part, via a computer program product, e.g., a computer programtangibly embodied in an information carrier, such as one or morenon-transitory machine-readable media, for execution by, or to controlthe operation of, one or more data processing apparatus, e.g., aprogrammable processor, a computer, multiple computers, and/orprogrammable logic components.

A computer program can be written in any form of programming language,including compiled or interpreted languages, and it can be deployed inany form, including as a stand-alone program or as a module, component,subroutine, or other unit suitable for use in a computing environment. Acomputer program can be deployed to be executed on one computer or onmultiple computers at one site or distributed across multiple sites andinterconnected by a network.

Actions associated with implementing all or part of the functions can beperformed by one or more programmable processors executing one or morecomputer programs to perform the functions of the calibration process.All or part of the functions can be implemented as, special purposelogic circuitry, e.g., an FPGA and/or an ASIC (application-specificintegrated circuit). Processors suitable for the execution of a computerprogram include, by way of example, both general and special purposemicroprocessors, and any one or more processors of any kind of digitalcomputer. Generally, a processor will receive instructions and data froma read-only memory or a random access memory or both. Components of acomputer include a processor for executing instructions and one or morememory devices for storing instructions and data.

In various implementations, electronic components described as being“coupled” can be linked via conventional hard-wired and/or wirelessmeans such that these electronic components can communicate data withone another. Additionally, sub-components within a given component canbe considered to be linked via conventional pathways, which may notnecessarily be illustrated.

A number of implementations have been described. Nevertheless, it willbe understood that additional modifications may be made withoutdeparting from the scope of the inventive concepts described herein,and, accordingly, other embodiments are within the scope of thefollowing claims.

We claim:
 1. A wearable audio device comprising: an acoustic transducerfor providing audio playback of an audio signal to a user; an internalmicrophone acoustically coupled to an ear canal of a user, wherein theinternal microphone generates an electrical signal responsive to anacoustic signal incident at the internal microphone; a proximity sensor;and a control circuit coupled with the acoustic transducer, the internalmicrophone and the proximity sensor, the control circuit configured to:determine a magnitude of an acoustic transfer function based on theelectrical signal and the audio signal at one or more predeterminedfrequencies; calibrate the proximity sensor; detect a change in thewearable audio device from one of: an off-head state to an on-headstate, or the on-head state to the off-head state using both thecalibrated proximity sensor and the magnitude of the acoustic transferfunction; and adjust at least one function of the wearable audio devicein response to detecting the change from the on-head state to theoff-head state or detecting the change from the off-head state to theon-head state.
 2. The wearable audio device of claim 1, wherein thecontrol circuit is configured to determine the magnitude of the acoustictransfer function during the audio playback to the user.
 3. The wearableaudio device of claim 1, wherein the control circuit is furtherconfigured to: measure a first transfer function based upon the audiosignal played back at the transducer and a control signal sent to thetransducer for initiating the audio playback; measure a second transferfunction based upon the audio signal played back at the transducer andthe electrical signal generated by the internal microphone; and based ona comparison between the first transfer function and the second transferfunction, detect a change in the wearable audio device from one of: theon-head state to the off-head state, or the off-head state to theon-head state.
 4. The wearable audio device of claim 3, wherein thecontrol circuit is configured to measure the first transfer function andthe second transfer function for each of a left side of the wearableaudio device and a right side of the wearable audio device, wherein thechange from the on-head state to the off-head state or from the off-headstate to the on-head state is detected only when both the left side andthe right side transfer functions are in agreement.
 5. The wearableaudio device of claim 1, wherein the proximity sensor comprises acapacitive proximity sensor or an infra-red (IR) sensor, and wherein theproximity sensor detects proximity to a head of the user to indicate thechange from the on-head state to the off-head state or from the off-headstate to the on-head state.
 6. The wearable audio device of claim 1,wherein the audio playback comprises at least one of: an audible feed oran interrogation signal.
 7. The wearable audio device of claim 1,wherein the control circuit is further configured to pause the audioplayback in response to detecting the change from the on-head state tothe off-head state.
 8. The wearable audio device of claim 1, wherein thepredetermined frequencies are below 400 Hz.
 9. The wearable audio deviceof claim 1, wherein the at least one function comprises an audioplayback function, a power function, a capacitive touch interfacefunction, an active noise reduction (ANR) function, a controllable noisecancellation (CNC) function or a shutdown timer function.
 10. Thewearable audio device of claim 1, further comprising a sensor systemcoupled with the control circuit for continuously operating during theon-head state, wherein the control circuit is further configured to:receive an indicator of an off-head detection event from the sensorsystem; and only in response to receiving the indicator of the off-headdetection event, confirm the off-head detection event by using thecontrol circuit to determine a magnitude of an acoustic transferfunction based on the electrical signal and the audio signal at one ormore predetermined frequencies to detect a change from one of: theon-head state to the off-head state, or the off-head state to theon-head state.
 11. The wearable audio device of claim 1, furthercomprising a sensor system coupled with the control circuit, wherein thecontrol circuit is further configured to: detect the change in thewearable audio device from one of: the on-head state to the off-headstate, or the off-head state to the on-head state from the determinedmagnitude of the acoustic transfer function; and confirm the off-headstate or the on-head state using the sensor system.
 12. Acomputer-implemented method of detecting a state of a wearable audiodevice on a user, the method comprising: detecting a change from one of:an on-head state to an off-head state, or the off-head state to theon-head state with a first sensor system, wherein the first sensorsystem comprises an internal microphone acoustically coupled to an earcanal of a user, wherein the internal microphone generates an electricalsignal responsive to an acoustical signal incident at the internalmicrophone, the detecting of the change from the on-head state to theoff-head state or the off-head state to the on-head state comprisingdetermining a magnitude of an acoustic transfer function based on theelectrical signal and the acoustical signal at one or more predeterminedfrequencies; calibrating a second, distinct sensor system; detecting achange from the other one of: the off-head state to the on-head state orthe on-head state to the off-head state using the calibrated secondsensor system, wherein the second sensor system comprises a proximitysensor; and adjusting an operating state of at least one function of thewearable audio device in response to detecting the change from theon-head state to the off-head state or detecting the change from theoff-head state to the on-head state.
 13. The computer-implemented methodof claim 12, further comprising: receiving an indicator of an off-headdetection event from an additional sensor system; and initiating thefirst sensor system to detect a change from the on-head state to theoff-head state in response to the indicator of the off-head detectionevent from the additional sensor system.
 14. The computer-implementedmethod of claim 12, further comprising: measuring a first transferfunction based upon the audio signal played back at a transducer at thewearable audio device and a control signal sent to the transducer forinitiating the audio playback; measuring a second transfer functionbased upon the audio signal played back at the transducer and theelectrical signal generated by the internal microphone; and based on acomparison between the first transfer function and the second transferfunction, detecting a change in the wearable audio device from one of:the on-head state to the off-head state, or the off-head state to theon-head state.
 15. The computer-implemented method of claim 14, furthercomprising measuring the first transfer function and the second transferfunction for each of a left side of the wearable audio device and aright side of the wearable audio device, wherein the change from theon-head state to the off-head state or the off-head state to the on-headstate is detected only when both the left side and the right sidetransfer functions are in agreement.
 16. A wearable audio devicecomprising: an acoustic transducer for providing audio playback of anacoustical signal to a user; an internal microphone acoustically coupledto an ear canal of a user, wherein the internal microphone generates anelectrical signal responsive to an acoustic signal incident at theinternal microphone; and a control circuit coupled with the acoustictransducer and the internal microphone, the control circuit configuredto: determine a magnitude of an acoustic transfer function based on theelectrical signal and the acoustical signal at one or more predeterminedfrequencies; pause the audio signal when a change from an on-head stateto an off-head state is detected; output an interrogation signal ornarrowband noise at the acoustic transducer while the audio signal ispaused; determine a magnitude of an acoustic transfer function based onthe electrical signal and the interrogation signal or narrowband noiseat one or more predetermined frequencies; and adjust at least onefunction of the wearable audio device in response to detecting one of: achange in the wearable audio device from the on-head state to theoff-head state or a change from an off-head state to the on-head state.17. The wearable audio device of claim 16, further comprising a sensorsystem coupled with the control circuit, wherein the control circuit isfurther configured to: detect the change in the wearable audio devicefrom one of: the on-head state to the off-head state, or the off-headstate to the on-head state from the determined magnitude of the acoustictransfer function; and confirm the off-head state or the on-head stateusing the sensor system.